Taste is a critical sensory system for sorting the rich array of potential foods in the environment into beneficial nutrient categories to be ingested, items not needed, and toxins to be avoided. There is an extensive research literature from a variety of species focused on gaining an understanding on how taste is capable of accomplishing this amazing feat for the health and welfare of the organism. There is a growing body of evidence that suggests that the gustatory system may be divisible into a small number of sub-modalities (e.g., sweet for carbohydrate, etc.), although the exact number awaits additional investigation. Further, a unique set of receptor mechanisms and group of neurons that are responsible for transmitting the information to the brain may serve each sub-modality. Our overall goal is to use extracellular single-cell recording techniques to define the number of sub modalities in the gustatory system and characterize their receptor and neural response properties. We have recently developed a new preparation for stable long-term recording of taste neuron responses. Our proposed recording studies will be from the geniculate ganglion of the facial nerve. Within the ganglion are the unipolar cell bodies of neurons that innervate the taste receptors on the tongue and palate. We propose to characterize the chemical and thermal sensitivity of the rat geniculate ganglion to lingual and palatal stimulation, and to examine the effects of specific pharmacological antagonists on taste transduction mechanisms. The rat will be studied because the vast background of neural and behavioral research comes largely from rats, it is an excellent model of human ingestion, and we have extensive experience with this species. The specific aims of this proposal are: (1) to characterize the responses of salt-sensitive and sweetsensitive neurons to a broad array of stimuli across several stimulus concentrations; (2) to examine the effects of specific pharmacological antagonists on salt and sweet transduction mechanisms; (3) to characterize the responses of various neuron groups to thermal stimulation and to assess taste-thermal interaction; and (4) to determine whether fat and protein can be included into primary taste traditionally restricted to sweet, salt, sour, and bitter.